Monday, July 6, 2009
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Database
1.Table (database)
In relational databases and flat file databases, a table is a set of data elements (values) that is organized using a model of vertical columns (which are identified by their name) and horizontal rows. A table has a specified number of columns, but can have any number of rows. Each row is identified by the values appearing in a particular column subset which has been identified as a candidate key.
Table is another term for relations; although there is the difference in that a table is usually a multi-set (bag) of rows whereas a relation is a set and does not allow duplicates. Besides the actual data rows, tables generally have associated with them some meta-information, such as constraints on the table or on the values within particular columns.
The data in a table does not have to be physically stored in the database. Views are also relational tables, but their data are calculated at query time. Another example are nicknames, which represent a pointer to a table in another database.
2.Database queries
The implementation of a database, its interface, and its query language is a project far too ambitious for the scope of this book and for the Objective CAML knowledge of the reader at this point. However, restricting the problem and using the functional programming style at its best allows us to create an interesting tool for query processing. For instance, we show how to use iterators as well as partial application to formulate and execute queries. We also show the use of a data type encapsulating functional values.
3.Database Form
A database form is a window or screen of related fields from a database.
It is used to enter data or browse and view data.
All forms contain a number of fields, each with a field-label. The field is a space to enter data. Forms layout the fields and field labels in a logical manner to make data entry user friendly.
In a database form the input is checked against the rules for the field-type and may be additional rules, such as not null. Forms may be also checked against field or table constraints defined in a database, such as foreign keys and table relationships.
OpenOffice.org Base can create database forms with the Form Wizard quickly.
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